CENSUS SAMPLING ERROR 



Sampling error in the census data results from the 

 nonresponse sample and the census sample data collec- 

 tion. Census items were classified as either complete 

 count or sample data items. In Alaska, all farms were 

 asked the complete count and sample items. The com- 

 plete count data items included land in farms, harvested 

 cropland, livestock inventory and sales, crop acreages, 

 quantities harvested and crop sales, land use, irrigation, 

 government loans and payments, conservation acreage, 

 type of organization, and operator characteristics (sections 

 1 through 22 of the census report form). The sample data 

 items included farm production expenditures, fertilizer and 

 chemical usage, farm machinery and equipment, value of 

 land and buildings, and farm-related income (sections 23 

 through 28 of the census report form). Variability in the 

 estimates of sample items is due both to the census 

 sample selection and estimation procedure and the non- 

 response sample estimation procedure.There is no sam- 

 pling error in Alaska since all farms were asked the sample 

 items and all nonrespondents were followed up to obtain a 

 response. 



CENSUS NONSAMPLiNG ERROR 



The accuracy of the census counts are affected by the 

 joint effects of the sampling errors described in the previ- 

 ous section and nonsampling errors. Extensive efforts 

 were made to compile a complete and accurate mail list for 

 the census, to design an understandable report form and 

 instructions, and to minimize processing errors through the 

 use of quality control, verification, and check measures on 

 specific operations. Nonsampling errors arise from incom- 

 pleteness of the census mail list, duplication in the mail list, 

 incorrect data reporting, errors in editing of reported data, 

 and errors in imputation for missing data. These specific 

 nonsampling errors are further discussed in this section. 

 Evaluation studies will be conducted to measure the extent 

 of nonsampling errors due to item imputation. 



Respondent and Enumerator Error 



Incorrect or incomplete responses to the mailed census 

 report form or to the questions posed by a telephone 

 enumerator introduce error into the census data. Such 

 incorrect information can lead, in some cases, to incorrect 

 enumeration of farms. To reduce all types of reporting 

 error, questions were phrased as clearly as possible based 

 on tests of the census report form, and detailed instruc- 

 tions for completing the report form were provided to each 

 addressee. In addition, each respondent's answers were 

 checked for completeness and consistency. 



Item Nonresponse 



Nonresponse to particular questions on the census 

 report that we would logically or statistically expect to be 

 present may create a type of nonsampling error in both 



complete count and sample data. When information reported 

 for another farm with similar characteristics is used to edit 

 or impute for item nonresponse, the data may be biased 

 because the characteristics of the nonrespondents have 

 not been observed and may differ from those reported by 

 respondents. Any attempt to correct the data for nonre- 

 sponse may not completely reflect this difference either at 

 the element level (individual farm operation) or on the 

 average. 



Processing Error 



The many steps of processing of each census report 

 form are sources for the introduction of nonsampling error. 

 The processing of the census report forms includes cleri- 

 cal screening for farm activity, computerized check-in of 

 report forms and followup of nonrespondents, keying and 

 transmittal of completed report forms, computerized edit- 

 ing of inconsistent and missing data, review and correction 

 of individual records referred from the computer edit, 

 review and correction of tabulated data, and electronic 

 data processing. These operations undergo a number of 

 quality control checks to ensure as accurate an application 

 as possible, yet some errors are not detected and cor- 

 rected. 



EDITING DATA AND IMPUTATION FOR ITEM 

 NONRESPONSE 



For the 1987 Census of Agriculture, as in previous 

 censuses, all reported data were keyed and then edited by 

 computer. The edits were used to determine whether the 

 reports met the minimum criteria to be counted as farms in 

 the census. Computer edits also performed a series of 

 complex, logical checks of consistency and completeness 

 of item responses. They provided the basis for deciding to 

 accept, impute (supply), delete, or alter the reported value 

 for each data record item. 



Whenever possible, edit imputations, deletions, and 

 changes were based on component or related data on the 

 respondent's report form. For some items, such as oper- 

 ator characteristics, data from the previous census were 

 used when available. Values for other missing or unaccept- 

 able reported data items were calculated based on reported 

 quantities and known price parameters. 



When these and similar methods were not available and 

 values had to be supplied, the imputation process used 

 information reported for another farm operation in a geo- 

 graphically adjacent area with characteristics similar to 

 those of the farm operation with incomplete data. For 

 example, a farm operation that reported acres of corn 

 harvested, but did not report quantity of corn harvested, 

 was assigned the same bushels of corn per acre harvested 

 as that of the last nearby farm with similar characteristics 

 that reported acceptable yields during that particular exe- 

 cution of the computer edit. The imputation for missing 



C-2 APPENDIX C 



1987 CENSUS OF AGRICULTURE 



